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How the Heart Works

The heart is a muscle responsible for pumping blood throughout your body. This page will teach you about how your heart works.

 Anatomy of the Heart

The heart is made of four chambers, the left and right atria, and the left and right ventricles. These chambers are separated by valves make sure the blood flows in the right direction. Blood from the body enters the right atrium and is pushed into the right ventricle. The right ventricle pumps the blood to the lungs where it picks up oxygen and returns to the left atrium. Blood moves into the left ventricle where it is pumped out to the entire body all the way to your fingers and toes; providing your body with the oxygen and nutrients it needs to keep you alive and healthy.


Arteries are the blood vessels in your body that carry blood AWAY from the heart. Veins are blood vessels that carry blood TOWARDS the heart.

Important Definitions

Acute Myocardial Infarction: Sometimes called heart attack. A heart attack occurs when low blood flow causes the heart to starve for oxygen. Heart muscle dies or becomes permanently damaged.

Aneurysm: A localized, blood-filled dilation (balloon-like bulge) of a blood vessel caused by disease or weakening of the vessel wall.

Angina Pectoris: Severe squeezing or pressure-like chest pain, brought on by exertion or stress. Usually a symptom of heart disease.

Aortic Aneurysm: A weakened and bulging area in the aorta, the major blood vessel that feeds blood to the body. A ruptured aortic aneurysm can cause life-threatening bleeding.

Arteriosclerosis: A group of diseases characterized by thickening and loss of elasticity of arterial walls. Sometimes called “hardening of the arteries”.

Atherosclerosis: A process in which deposits of yellowish plaques (atheromas) containing cholesterol and other materials are formed within arteries. An atheroma can increase in size and harden over time reducing blood flow. It can potentially result in bleeding into and subsequently clotting of an artery resulting in a heart attack.

Body Mass Index (BMI): A measure of human body size and proportion. It is defined as the weight in kilograms divided by the square of height in meters.

Cardiovascular Diseases: Cardiovascular disease refers to the class of diseases that involve the heart or blood vessels (arteries and veins).

Cerebrovascular Disease: Any disease by which the arteries in the brain, or are connected to the brain, are defective. Frequently used interchangeably with the term “Stroke.”

Cholesterol: Cholesterol is a waxy, fat-like substance that occurs naturally in all parts of the body. Elevated LDL cholesterol levels are associated with atherosclerosis.

Congestive Heart Failure: A condition in which the heart can’t pump enough blood to the body’s other organs. The “failing” heart keeps working but not as efficiently as it should.

Diabetes: Diabetes is a disease of insulin production and utilization. There are two major classifications, insulin dependent diabetes (IDD) or type I and non-insulin dependent diabetes (NIDD) or type II. Diabetes is a risk factor for cardiovascular disease.

Embolism: The sudden blocking of an artery by a clot or foreign material which has been brought to the site by the blood current.

Exercise Stress Test: A diagnostic test done on a treadmill during which the workload on the heart will gradually increase as the speed and height of the treadmill are increased at three-minute intervals.

Hypertension (High Blood Pressure): Generally defined as diastolic (when the heart is relaxing) blood pressure equal to or greater than 90 mm HG or systolic (when the heart is pumping) blood pressure equal to or greater than 140 mm HG. Hypertension is a risk factor for cardiovascular disease.

Ischemic Heart Disease: Any condition in which heart muscle is damaged or works inefficiently because of an deficiency of blood supply, most often caused by atherosclerosis. Also called coronary heart disease (CHD).

Lipoproteins: A combination of cholesterol and protein that is used to transport cholesterol through the blood stream. High-density lipoproteins (HDL) are known as “good” cholesterol, while low-density lipoproteins (LDL) are known as “bad” cholesterol.

Necrosis: Cellular death affecting groups of cells, part of a structure or an organ

Obesity: A relative term for excessive accumulation of fat in the body, a generally accepted measure of obesity is having a body mass index (BMI) greater than or equal to 30. Obesity/physical inactivity are risk factors for cardiovascular disease.

Occlusion: Coronary occlusion is the complete obstruction of an artery of the heart, usually from atherosclerosis.

Physical Inactivity: A relative term which refers to lack of exercise or a sedentary lifestyle. Obesity/physical inactivity are risk factors for cardiovascular disease.

Risk Factor: A risk factor is an attribute which is associated with an increased probability of a disease.

Sedentary Lifestyle: Loosely defined as low levels of physical activity over extended periods of time. Lack of physical exercise is a risk factor for cardiovascular disease.

Smoking: Inhaling cigarette smoke. Smoking is a strong risk factor for cardiovascular disease.

Stenosis: Narrowing or constricting of a duct, canal or blood vessel.

Stroke: A condition that results in a disruption of blood flow to a region of the brain causing irreversible “death” of brain tissue. This can be due to ischemia (lack of blood supply) caused by thrombosis (blood clot) or embolism (blockage), or due to a hemorrhage (bleeding).

Thallium Test: A Thallium Stress test looks at the blood flow to your heart muscle at rest and during stress. During a stress test, a radioactive material called Thallium is injected into a vein. A gamma camera takes pictures of the Thallium in the heart and areas of abnormal blood flow are identified.

Thrombus (Thrombosis): Commonly referred to as a blood clot frequently causing a blockage in a blood vessel.

Waist-Hip Ratio: The ratio of waist circumference (cm) to hip circumference (cm). It is used as a measurement of obesity.